Transmission system



Oct. 4, 1927, 1,644,395

B. G. POHLMANN TRANSMISSION SYSTEM Filed May 29. 1926 atente Get. 4,l2?.

BRUNO G. POHLMANN, F SIEMENSSTADT, NEAB BERLIN, GERMANY, ASSIGNOR TOSIEMENS & HALSKE AKTIENGESELLSCHAFT, OF SIEMENSSTADT, NEAR B l It',

GERMANY, A CORPORATIVIION 0F GERMANY.

TRANSMISSION SYSTEM.

Application filed May 29, 1926, Serial No. 112,419, wand, in Germany May14, 1925.

This invention relates to electrical transmission systems and has forits general ob'- ject to compensate for the distortion produced by along transmission line.

5 As is well known. the distortion of long telephone lines is eliminatedeither by using repeaters having amplification characteristicsproportioned to compensate for the line distortion o1' by insertingcorrecting artificial lines having attenuation characteristicscomplementary to the attenuation of the line in combination withrepeaters having substantially flat amplification characteristics. Inboth cases an overall characteristic which is independent of frequencyis desired. Generally the line is divided 'into sections and thedistortion in each section is corrected by the corresponding repeater orthe equalizer associated therewith. In long.

transmission lines. which necessarily embrace a large number lofrepeater sections, the demands made on the precision of correction ateach individual repeater point are exceedingly high since any deviationsfrom 25 the attenuation or amplification characteristic required, which`may be produced by slight inaccuracies in the correcting means, likelyoccur at each repeater in the same frequency regions and consequentlyare cumulative for the entire transmission system.

A particular obj ect of this invention is to overcome this difficulty. r

Therefore. in accordance` with one feature of the inventionthe-correcting means of the sections comprising the transmission systemare made diiferent, the differences being such that the sections arecomplementary to each other giving an overall transmissioncharacteristic which is substantially inde- 40 pendent of frequency.

tion in a system comprising a large number of sections, each of a groupof sections is corrected to give an approximately constant 4 5characteristic and there is associated with one section of thev groupanadditional cor-- recting means having such a characteristic as tocompensate for the combined discrep ancies of the group.

lf the transmission system is ofv such length that it embodies severalgroups of sections of similar design the yariations from the. desiredcharacteristic in each group may be' cumulative in a similar manner asIn a preferred embodiment of the inven-l the variations in the sectionsof each group so that it is desirable `to provide additional means to.compensate for the total. group inaccuracies within the system in thesame manner as the total section inaccuracies are compensated in eachgroup. If the system 1s of such length that itis desirable to regroupthe grou s this method may be extended still furt er.

Since, from a design standpoint, itis desirable to keep the correctingmeans as unitary as possible, an attempt is made to adhere to thisprinciple so far as possible without deviating' from the spirit of theinvention. Thus-within a section, group, or system. all sections orgroups but one can be similarly constructed, their associated correctingmeans rbeing so designed that an overall substantially constantcharacteristic 1s obtained. If correcting repeaters are eni ployed therepeaters can either be particularly designed so that ends upon thefrequency in a manner diferent from the standard repeaters, or else arepeater of the standard type having s ecial associated'corr'ectingmeans can be use The spacing of the special repeater points ispreferably so chosen that the net distortion over the portion of theline therebtween is of the v'same order of magnitude as is ordinarilycorrected for with a single network.. In this way apractically completecorrection is obtained, even with very gre-at lengths of line. without`extraordinary demands be ing made upon the correcting means at thespecial repeater points.

`A limiting case is the one in which the group lconsists of only twosections in which the errors of'correction are so displaced with respectto each otherthat they practically neutralize one another. Atransmission system of a large number of sections is then comprised ofmere groups of two sections each so that altogetherit'is only necessaryto construct two types of correcting means,

except where with an extraordinarily` large lnumber of groups anelimination of systematic errors of correction is again necessary.

rlhese and other. objects, features and aspects of the invention can bemore readily understood by reference to the following detailed descrition of one particular embodiment of the invention in connection withthe ldrawing in which:

the amplification deioo viii

Fig. 1 shows-graphically the attenuation and amplificationcharacteristic of a single line'section and repeater.

Fig. 2 shows graphically the netdistortion in a group of correctedsections and Fig. 3 shows diagrammatically one embodiment of atransmission system according to this invention.

Curve b of Fig. l shows the attenuation characteristic of a singlerepeater section plotted against frequency, while curve s of the sainefigure shows the amplication characteristic of a correcting repeaterassociated with the same section plotted against frequency. It will ybenoted that the deviationsrof the lamplification curve from theattenuation curve are fairly small giving a characteristic for a singlesectionwhich is a proximately lconstant with frequency.l

urve b, of Fig. 2, however, shows the net equivalent curve for sixrepeater sections,

the inaccuracies in the six sections having added up to give acharacteristic which is suiiiciently distprted .to disturb speechtransmission.

Fi 3 shows a transmission system compose of six line sections 1, 2, 3,4, "5 and 6' and associated repeaters, 11, 12, 13, 14,

and 16. Assumingth'atthe attenuation in each section is represented bythe' curve b of Fig. 1, it has been found desirable for carrying `outthis invention to design thereeaters to have an amplificationcharacteristic s somewhat higher thansA which would beirequired forcompensating for the attenuy ationl of a single section. This gives atotal attenuation characteristic 'for the six sections as shown-by thecurve b,. Associated with'the sixth repeater 16 is a network e vcomposed.of two tuned circuits e, and e2 each designedto be resonant at one ofthe minima of the curve "6".. to give an overallv .characteristic asshown by the curve b, of

. a secon 2 which is substantially independent of frequenc At the leftof Fig. 3 is shown correcting network e associated with the ,preceding,group of 'repeater sections. Obviously instead of using .tuned circuitother types of well known correcting networks may be` employed iii placethereof.

This invention is not limited to the particular embodiment shown'ibutmay be variously modified; for example, as described generally above.Similar arrangements may also .be used for correcting for phase distor-`tion or for both phase distortion and attenuation.

lVhat is claimed is: 1. A transmission system comprising a line of aplurality of groups of sections, at-.

tenuation 'correctingmeansassociated with each of a group of sections togive each of said sections similar transmission characteristicsapproximately independent of frequency and means associated with eachgroup of sections Ito substantially compensate for the net variation Pofthe total transmis?v sion characteristic of said group of sectionsl fromthe desired constant,frequency-transmission characteristic. l 'A 2. Atransmission system comprising a multiplicity of tandem sections withamplifying repeaters connectedlbetween successive sections, means associatedwith certain repeaters at points along'tlie system forcorrecting for unequal attenuation of dii'erent frequency components,transmitted by the system, and means associated with repeaters atpoints respectively intermediate said eerthe net attenuation of,`saidsystemincluding the other repeatersA and'theirassociated'correcting-means, whereby substantially complete correctionis` madel at a number of' line a pluralityv'of sections apart,correcting for the net distortion lresulting after the first-mentionedcorrecting steps.

In'witness whereof, I hereunto subscribe my name this-28th day of April,A. D., 1926 BRUNO .`G.' POHLMANN.

tain repeaters proportioned with respect to 30 l

